Player View Distance Controller

• Add /pvdc shortcut subcommand
• Backend performance improvements
• Chunks set by others should be reset when setting own view distance
• Retrieve existing PlayerDataHandler instance instead of creating a new instance
• Switch HashMap to ConcurrentHashMap to ensure thread safety
• Add more defensive design for the event of config folder deletion
• Bug fixes and small changes

Full Changelog: https://github.com/Wyzebb/PlayerViewDistanceController/compare/v2.0.2...v2.1.0